Developing, correct, the acorn is the oak tree at seed stage just as the foetus is the human being at foetal stage. This is why you are wrong because you deny the reality.Your "developing" is correct. An acorn is not an oak tree, it is an acorn. It develops into an oak tree, but it is not itself an oak tree.
I am not pretending either. A placenta develops from the zygote in the same way that a baby does, and a placenta is not a human being. The property of "developing from a zygote" is not sufficient to define a human being.
Also my point was the placenta is not the human being which you seem to have agreed to, but you deny the human being at zygote stage is a human being, which is your error.